The goal of this project is to examine dysfunction of preattentive and attentive regulatory mechanisms in children and infants who exhibit disturbance in the modulation of cognitive, affective, and social processes. Actions of these regulatory mechanisms are assessed through examination of steady-state autonomic and central nervous system activity and of the response of these systems to environmental events. Measurement of the blink reflex, heart rate, respiration, and task performance during rest and in response to simple two-stimulus paradigms permit assessment of the integration of different neural systems (sensory, motor and autonomic), preattentive inhibitory and excitatory effects on sensory processing, and different components of attention including intensity, maintenance, breadth (focus or selectivity), and resistance to distraction. Data collection has continued in a studies of regulatory functioning in groups of 7-to-12-year-olds with various neuropsychiatric disorder. Results of analyses of preattentive processing in a group of 30 children with Attention-deficit hyperactivity disorder (ADHD) indicate greater difficulties in brainstem-mediated regulation for ADHD without co-occurring conduct and aggressive problems.